Hydrogels, primarily due to their relatively high water content, have been used in tissue engineering and drug delivery, and can allow for nearly free diffusion of drugs and/or nutrients. Hydrogels can be modified readily with a range of chemical functionalities, which may impart at least one of bioactivity, controlled degradability, and a variety of pore sizes.
Hydrogels also can be advantageous due to their ability to be injected in a fluid state, conform to the shape of a tissue, and/or be solidified in situ using a variety of chemical and physical crosslinking methodologies. The crosslinking methods often can be extended to create hydrogels that are cohesive and capable of adhering to a surrounding tissue, thereby possibly enhancing tissue-biomaterial integration.
Hydrogels, however, generally have weak mechanical properties, e.g., modulus, toughness, and/or strength, compared to many biological tissues. Most hydrogels are quite brittle and weak. Although the modern material design of some hydrogels has been aimed at improving toughness and stiffness through the use of composites, the resulting hydrogels still tend to be too weak for mechanically demanding applications within the body. As a result, hydrogels frequently are applied only to softer tissues. Also, some injected hydrogels flow too readily prior to gelation, thereby complicating their implantation in wet conditions or in difficult geometries.
There exists a need for hydrogels that have mechanical properties that permit their use with a number of different tissues in a variety of locations.